This application is directed to coatings for ionographic or electrophotographic, including digital and image on image, imaging and printing apparatuses and machines, and more particularly is directed to coatings for donor members such as those donor members including electrodes closely spaced therein to form a toner powder cloud in a development zone to develop a latent image. The application is directed, in embodiments, to suitable conductive and semiconductive overcoatings, for donor member or transport members like scavengeless or hybrid scavengeless development systems. In embodiments, the coatings comprise nano-size powders.
Generally, the process of electrophotographic printing includes charging a photoconductive member to a substantially uniform potential so as to sensitize the photoconductive surface thereof. The charged portion of the photoconductive surface is exposed to a light image of an original document being reproduced. This records an electrostatic latent image on the photoconductive surface. After the electrostatic latent image is recorded on the photoconductive surface, the electrostatic latent image is developed. Two component and single component developer materials are commonly used for development. Toner particles are attracted to the latent image forming a toner powder image on the photoconductive surface, the toner powder image is subsequently transferred to a copy sheet, and finally, the toner powder image is heated to permanently fuse the toner powder image to the copy sheet in image configuration.
One type of development system is a single component development system such as a scavengeless development system that uses a donor roll (donor member) for transporting charged toner (single component developer) to the development zone. At least one, and in embodiments, a plurality of electrode members, are closely spaced to the donor member in the development zone. An AC voltage is applied to the electrode members forming a toner cloud in the development zone. The electrostatic fields generated by the electrostatic latent image attract toner from the toner cloud to develop the electrostatic latent image.
Another type of development system is a two-component development system such as a hybrid scavengeless development system which employs a magnetic brush developer member (magnetic member) for transporting carrier having toner (two component developer) adhering triboelectrically thereto. A donor member is used in this configuration also to transport charged toner to the development zone. The donor member and magnetic member are electrically biased relative to one another. Toner is attracted to the donor member from the magnetic member. Electrically biased electrode members detach the toner from the donor member forming a toner powder cloud in the development zone, and the electrostatic latent image attracts the toner particles thereto. In this way, the electrostatic latent image recorded on the photoconductive surface is developed with toner particles.
Coatings on the donor member can lead to various problems. For example, there can be a toner filming problem on the donor member. Filming consists of toner adhesion to the outside of the donor member, rendering it insulative, and reducing developability. Filming can dramatically reduce the donor member life. For example, donor member life can be reduced to from 20 million copies, to between 55,000 and 750,000 copies. Analysis of donor members has shown toner particles that have fused themselves into small pores and micro cracks on the surface of the ceramic coating. Once a single toner particle is fused into a pore, other toner particles migrate to the pore and attach themselves, which causes filming. It has been shown that less porous or non-porous films do not tend to have the toner filming problem.
U.S. Pat. No. 6,355,352 teaches use of a nano-size zinc oxide (Col. 8, line 62) in a layer of a marking member, wherein the nano-size filler has a particle size of from about 1 to about 250 (0.1 micrometers to 100 nanometers).
U.S. Pat. No. 6,300,027 teaches a photoreceptor having a hydrophobic silica having an average particle diameter of from about 1 to about 60 nanometers, preferably from about 7 to about 40 nanometers (col. 4, lines 54-57).
U.S. Patent Published Application 2003/134209 discloses at paragraph 207 use of alumina having a particle size of 45 nanometers in a protective layer of a charge transport layer of a photoreceptor.
U.S. Pat. No. 5,008,167 teaches a metal oxide having a particle size of 30 to 1,000 angstroms (3 to about 100 nanometers) in an imaging device (col. 14, lines 25-29).
U.S. Pat. No. 5,714,248 discloses an imaging member having a particle size of 10 to about 10,000 nanometers (col. 5, lines 57-62).
Therefore, there exists a need for a donor member coating which provides conductivity or resistivity within a desired range, and which has a coating that is less porous or non-porous. It is further desired that the donor member have wear-resistant properties so that the surface will not be readily abraded by adjacent surfaces. Further, it is desirable that the surface of the donor member be without anomalies such as pinholes, which may be created in the course of its manufacture. Pinholes created in the manufacturing process or caused by abrasions during use, can result in electrostatic “hot spots” and undesirable electrical arcing in the vicinity of such structural imperfections. It is an additional desired feature that the donor member have “uniform conductivity.” Other physical properties of the donor member, such as the mechanical adhesion of toner particles, are also desired.